Instrumentation and Controls Design and Maintenance Strategy for Small Modular Reactors

Small Modular Reactors (SMRs) under design and development today are working to crystallize the measurements that must be made to control the reactor and monitor its safety. Traditionally, temperature, pressure, level, flow, and neutron flux are measured in conventional nuclear reactors for operation and control and to protect against equipment and process deviations that can affect safety. In most current SMR designs, essentially the same process variables may have to be measured; especially primary coolant flow depending on whether the core cooling and heat transfer results from natural circulation or forced flow. The flow can be measured directly or inferred from other measurements or estimated through empirical or physical modeling. The conventional sensors that are qualified for nuclear services and are currently used in nuclear power plants may or may not be suitable for SMRs. It all depends on the size and qualification requirements, installation details, static and dynamic performance specifications, wiring details, and sensor life expectancy. This paper will explore the possibilities that exist for SMRs to use today’s sensors and any need for new sensor designs. In addition, the paper will identify new means for automated monitoring of instrumentation and control (I&C) sensor performance in SMRs. In particular, the existing array of online calibration monitoring techniques and in-situ response time measurement methods will be evaluated for implementation in SMRs. This is important at this early stage as SMRs can easily build provisions in their mechanical, electrical, and I&C designs to accommodate online and automated I&C maintenance. For example, it is envisioned that SMRs will not be performing periodic sensor calibrations using classical hands-on procedures. Rather, SMRs are expected to be equipped with new technologies to verify the I&C performance automatically and flag the sensors and systems to be calibrated, response time tested, repaired, or replaced. The paper will explore these possibilities and will report on a current R&D project that is underway at AMS with funding from the U.S. Department of Energy (DOE) with the goal to adapt the existing online monitoring (OLM) technologies for implementation in SMRs. The existing OLM technologies have been used by AMS in commercial nuclear power plants and research reactors for monitoring of I&C equipment performance including calibration, response time, detection of sensing line blockages, and to distinguish whether a signal anomaly is due to cables/connectors, electromagnetic interference, an end device being a sensor or a pump, other rotating equipment, etc.